4.2. Post natal skull development in small African
Pangolins
Samples obtained from Ibadan geo-location in (Fig. 3a) demonstrated more
robust size and shape variations; being more disposed on the first axis
of the PCA plot with size contributing a higher proportion of variations
observed in comparison to similar samples from Kwara and Makurdi
locations where shape variations factor overrode as they are better
disposed on the second axis of the plot. Between the groups (Fig. 3b),
the observed differences perhaps explain the input of environment on
skull phenotypes development (Elliot, 2010; Benitez et al., 2020). Skull
samples from Makurdi demonstrated the highest population variation in
both size and shape factors compared to those from other geo-ecologies.
Environmental prevailing temperatures, vegetation and diet variables as
well as predator influences seem to favor samples from Ibadan
eco-environments when compared to those from Guinea and Sudan savannah
(Kwara and Makurdi) respectively. Large areas of overlap existed between
the samples evaluated as shown in the MANOVA and ANOSIM analyses which
failed to discriminate the species on geographical bias and was
confirmed similar respectively; this is indicative of topographical area
landmark similarity among population evaluated, such areas did not give
any untoward developmental signal but follow phylogenetic trajectory
compared to areas of non-overlap and is consistent with the report on
similar extant species (Ferreira-Cardoso et al., 2020).
Skull structural flexibility potentials may have been exhibited by
certain trait-variability patterns in these studied samples ontogeny
which may be consequential in evolutionary trend. (Fig. 3b, Tables 1 and
2) confirmed the suggestion of Hendrikse et al. (2007) where subtle
rostrum and dorsal skull deviations from midline (Fig. 4) were
detectable and attributable to genetic input and lateralization in
muscle load use or other functional demands (Urbanova et al., 2014).
Maximum size and shape overlap observed (Fig. 3b) among sample
populations from the geo-locations suggests high similarity this was
further confirmed by an analysis of similarity (ANOSIM) and a
multivariate analysis of variation (MANOVA) (Fig. 3c) on both skull
views understudied. Rostrum shape overlaps between the rainforest
(Ibadan) and Guinea savannah (Kwara) samples seem to progress in
diversity as the species geographical space goes northwards to the Sudan
savannah belt, they are however not been reported in the Sahel.
During craniofacial development, cranial neural crest cells’ migration
to (frontal part of head) generate the facial skeleton (Le Douarin and
Kalcheim, 1999) to become the mesenchyme of future face while the back
of the skull is derived from a combination of neural crest-derived and
mesodermal bones (Murphy et al., 2001a). Skull bones are derived from
both the neural crest and the head mesoderm (Le Lievre 1980; Noden 1978;
Klingenberg, 2010). Results from our study exposed some unexplained
cranial asymmetries among the population investigated likely to be
consequential to inconsistencies in cellular migrations; this is the
most probable explanation to the observed unapparent skull asymmetries
despite the absence of masticatory function in this species.
Furthermore, the ecologic definition of arboreal living in species’
habitat substrates to their cranio-facial morphotypes with compensatory
mechanisms in skull morphologic equilibrium as adaptations to their
peculiar environment (Ritchsmeier & Deleon, 2009); though insignificant
(F1539=3.4045, F882= 3.2665); for the
skull views evaluated respectively demonstrated surreptitious
fluctuating asymmetry (FA) (Tables 1 and 2); a measure of developmental
instability (Klingenerg and McIntyre, 1998) in minute randomly
distributed anomalies associated with environmental signals (Urbanova,
2014) on either (right and left) sides of skulls in the population
evaluated in an otherwise bilateral development This is further
substantiated by foramen magnum asymmetry assessments where size was an
overriding factor (table 6) over shape.
Occurrences of FA in paired body structures have been attributed to
ecologic, habitat, on-going metabolic disease conditions among
population groups (Singh and Rosen, 2001). It is also known that a
sustained unilateral body-side muscular load demand preference would
directly modulate external observable morphology (Urbanova, 2014).
Results from this study only confirmed a weak occurrence of FA
(F=0.00034755). Foramen magnum development in the current study further
predicated its importance in accurate forensic analyses, types of
abnormalities encountered, proportions and interpretations in
embryologic and evolutionary contexts among species as well as
allometric trajectory pattern discriminations. Such information has no
priory literature evidence in Pangolins. Salient neurological,
developmentally consequential information hitherto not described could
be inferred from the results obtained from EFA; the dorsal-most rim,
right dorso-lateral, left dorso-lateral portions presented the
discriminating areas of individual shape variations (Fig. 6, Table 6).
Manoel et al. (2009) documented the possibility of cerebellar protrusion
resultant upon volume reduction of the posterior fossa (pre and post
natal); syringomelia and other neurological disorders sequel to foramen
magnum dysmorphology manifested by the occurrence of dorsal notches as a
result of developmental errors. Such structural malformations have been
associated with domestication attempts and captive breeding of species
(Dixon et al., 1997; Hewitt, 2011); this finding satisfies the
4th objective of this study. The results of the
present investigation notwithstanding; is limited by an absence of fetal
skulls thus prenatal studies will further confirm the onset and form of
asymmetries in these pangolins.